The characteristics, advantages and disadvantages of emulsion polymerization, solution polymerization, suspension polymerization and bulk polymerization were compared.

Characteristics of four polymerization methods:

Emulsion polymerization is characterized by dispersing monomers in water by emulsifier and mechanical stirring to form emulsion, and then adding initiator to initiate monomer polymerization.

The characteristic of solution polymerization is that the monomer is dissolved in an appropriate solvent, and the initiator (or catalyst) is added in solution.

The characteristic of suspension polymerization is that the monomer dissolved with initiator is suspended in water in the form of droplets for free radical polymerization.

The characteristic of bulk polymerization is that monomer polymerization is initiated by initiator or itself under the action of light, heat and radiation without adding solvents and other dispersants.

Advantages and disadvantages of four polymerization methods:

I. Emulsion polymerization

Advantages: high polymerization speed and high molecular weight of products; Using water as the medium of dispersant is beneficial to heat transfer and temperature control; The viscosity of emulsion polymerization system is still very low after the reaction reaches high conversion rate, and the dispersion system is stable and easy to control, realizing continuous operation. Latex can be directly used as the final product.

Disadvantages: the separation and precipitation process of polymer is complicated, and demulsifier or coagulant needs to be added; The reactor wall and pipeline are easy to stick; There are many kinds of additives, and the dosage is large, and there are many impurities left in the product. If the washing is not clean, the physical properties of the product will be affected.

Second, solution polymerization.

Advantages: the polymerization heat is easy to diffuse and the polymerization temperature is easy to control; Can be directly completed in solution; After the reaction, the material is easy to transport; Low molecular substances are easy to remove; The phenomenon of automatic acceleration can be eliminated. Water solution polymerization takes water as solvent, which is very beneficial to environmental protection.

Disadvantages: monomer is diluted by solvent, the polymerization speed is slow, and the molecular weight of the product is low; Large solvent consumption, solvent recovery and treatment, low equipment utilization rate, resulting in increased costs; The use of solvents leads to environmental pollution.

Thirdly, suspension polymerization.

Advantages: the viscosity of the system is low, the polymerization heat is easy to export, and the heat dissipation and temperature control are easier than bulk polymerization and solution polymerization; The relative molecular weight and its distribution of the product are relatively stable, the polymerization rate and relative molecular weight are higher than those of solution polymerization, and the impurity content is lower than that of emulsion polymerization. Post-treatment is simpler than solution polymerization and emulsion polymerization, with low production cost and less three wastes; Granular resin can be directly used for processing.

Disadvantages: there is automatic acceleration; Dispersants must be used, which are difficult to be removed from polymer products after polymerization, which will affect the performance of polymer products (such as appearance, aging performance, etc.). ); Polymerization product particles will contain a small amount of monomer, which is not easy to be completely removed, affecting polymer properties.

Fourthly, bulk polymerization.

Advantages: the product is pure and can be directly cast and molded; The production equipment utilization is high, the operation is simple, and complicated separation and purification operations are not needed. Less investment, large effective reaction volume of the reactor, large production capacity, easy continuous operation and low production cost.

Disadvantages: the thermal effect is relatively large. Automatic acceleration will cause foaming and discoloration of the product. In severe cases, the temperature is out of control, causing explosion and aggregation, and the product is more difficult to meet the standard. Because the viscosity of the system increases with the progress of polymerization, it is difficult to mix and transfer heat, and sometimes the polymerization speed will automatically increase. If it is not properly controlled, it will cause explosive polymerization. The molecular weight distribution of the product is wide, the unreacted monomer is difficult to remove, and the mechanical properties of the product are poor.

Extended data:

Emulsion polymerization was first invented by Germany. During World War II, the United States used this technology to produce styrene-butadiene rubber, and then successively produced nitrile rubber, chloroprene rubber, polyacrylate latex, polyvinyl acetate latex (commonly known as white rubber) and polyvinyl chloride.

Different from suspension polymerization, emulsion system is relatively stable, and there are batch, semi-batch and continuous production in industry. When transported or stored by pipeline, it will not be stirred or layered. In production, the polymerization speed, molecular weight and particle size of colloidal particles can also be controlled by "seed polymerization" (that is, latex containing active chains) and adding monomers or regulators. High concentration latex can also be directly produced.

Suspension polymerization is mostly free radical polymerization at present, but it is widely used in industry. For example, 75% of PVC production adopts suspension polymerization process, and the polymerization kettle is getting bigger and bigger; Polystyrene and styrene polymers are mainly produced by suspension polymerization; Others include polyvinyl acetate, polyacrylate, fluororesin, etc.

Polymerization is carried out in enamel kettle or stainless steel kettle with jacket, and the operation is intermittent. In addition to heat transfer through the jacket, the cauldron is also equipped with an internal cooling pipe or (and) a top condenser, and the heat transfer coefficient is improved as much as possible. The viscosity of suspension polymerization system is not high. Generally, small-sized high-speed turbine, paddle and three-blade paddle are used for stirring.

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